Interrupting device employing a controller for regulating contact closing speeds



July 3, 1956 L P ,753,424

H. 2 INTERRUPTING DEVICE EMPLOYING A CONTROLLER FOR REGULATING CONTACT CLOSING SPEEDS 3 Sheets-Sheet 1 Filed March 10, 1955 y 3, 1956 H. L. PEEK INTERRUPTING DEVIC FOR REGULATI 2,753,424 a EMPLOYING A CONTROLLER NG CONTACT CLOSING SPEEDS 5 Sheets-Sheet 2 Filed March 10, 1953 H. PEEK 2,753,424 VICE EMPLOYING A CONTROLLER NTACT CLOSING SPEEDS 3 Sheets-Sheet 5 INTERRUPTING DE FOR REGULATING CO 95:5

July 3, 1956 Filed March 10,

United States Patent INTERRUPTING nnvrcn EMPLOYING A CON- rnorrunroanncumrnse CONTACT crosnro SPEEDS Henry L. Peek, Boston, Mass., assiguor to Allis-Chalmers Manufacturing Company, Milwaukee, Wis.

Application l /iarch 10, 1953, Serial No. 341,467 11 Claims. (Cl.'200 -150) This invention relates to electric power interrupting devices and'more'particularly to a circuit'breaker structure employing means for controlling the velocity of its movable contacts.

Heretofore, circuit breaker structures used shock absorbers of one form or another to control the opening and-closingspeeds of the circuit breakers movable contacts. These shock absorbers were used to'absorb or dissipate in some manner the kinetic energy that the contact-structureacquired during its movement. These prior art structureswere actuated at high speeds and gradually and'substantiallycompletely absorbed the kinetic energy of the movable contact structure.

This type of shock absorber was incapable of performing in the modern circuit breakers the type of required circuit breaker contact controlling action. Many of the present day breakers use interrupting structures employingspring actuated interruptingcontacts'such as pressure generating contacts alone, and in'combination with spring actuatedoilpumps for the interruption ofline charging currents and such low values of inductive current as are not effectively interrupted by suicidal type devices. These interrupting'contact springs and'the' oil pump springs impose extremely heavy loads near the end of the closing stroke of the circuit breaker structure, thusrequiring high pressures to effect the final'closing action of the structure. If these high pressures acted'uncont'rolled throughout the closing stroke of the circuit breaker with nothing but the mass of the movable members to act upon, extremely high velocity impacts would result. If the prior art shock absorber structures were relied on to control the speed of operation of the contacts they would'retard the' movement of the structure during substantially the full stroke of the shock absorber so that the contacts could not overcome the heavy spring loads at the ends of their stroke and the circuit breaker structure would fail because it could not complete the electric circuit.

In accordance with this invention a new and improved circuit breaker structure is provided in which the velocity of the circuit breaker movable contact structure is limited to eliminate the possibility of damage due to high velocity impacts; Since it has been found that approximately half of the circuit breaker stroke is required to attain velocities that might be damaging, only part of the closing stroke of the contact structure requires control, namely that part between the contact open position and that point at which the heavy closing loads are encountered.

It is, therefore, one object of the present invention to provide a new and improved circuit breaker structure in which high velocity impacts at the end of the circuit breaker closing strokes are prevented.

Another object of this invention is to provide a new and improved circuit breaker structure employing a contact speed controller which offers high retarding forces to high velocities of the movable contact structure but negligible retarding forces to low velocities of the movable contact structure.

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A further object of this invention is to provide a new and improved circuit breaker structure in which the contact structure is retarded during its initial acceleration in contact closing direction but unrestrained during the latter part of its stroke when it engages the closing loads.

A still further object of this invention is to provide a new and improved circuit breaker structure in which the contact actuating structure is restrained until the contact closing loads are encountered.

A still further object of this invention is to provide a new and improved circuit breaker structure in which the high velocity impacts which occur at the time the con tact actuating structure engages the movable contact spring biasing means is prevented.

Objects and advantages other than those set forth will be apparent from the following description when read in connection with the accompanying drawings, in which:

Fig. 1 is a view partly in section of a circuit breaker structure and its operating mechanism embodying the present invention shown in the closed position;

Fig. 2 is an enlarged cross sectional view of a part of the circuit breaker structure shown in Fig. 1;

Fig; 3 is an enlarged cross sectional view taken along line III-III of the pole unit tripping mechanism shown in Fig. 1;

Fig. 4 is an enlarged sectional view of the speed controller shown in Fig. I assumed to be in contact open position; and

Fig. 5 is a cross sectional view of the speed controller shown in Fig. 4 taken along the line VV.

Referring more particularly to the drawings by characters of reference, Figs. 1 to 5 illustrate a device comprising a circuit breaker 1G, a pneumatically operated trip free mechanism 11 and a speed controller 12. The pneumatically operated trip free mechanism 11 comprises any suitable motor such as a pneumatic motor 13 which may be of the cylinder and piston type, and a trip free linkage 14. Motor 13 and circuit breaker 10 are operatively connected by linkage 14.

The oil circuit breaker 10 shown in Figs. 1 and 2 is of the high voltage type, such as that used in power transmission systems. The circuit breaker in is enclosed by an oil tank '2. High voltage insulating bushings l5 and 16 are each connected at one end thereof to lead-in conductors of a power system (not shown) and are each attached at their other end to interrupting chambers 1'7 and 18.

For cooperation with the fixed contact structures 19 and 2% a movable bridging contact member 21 and its movable contacts 27. and 23 mounted thereon are vertically actuated by an insulating operating or lift rod 24 to make and break the power circuit within the interrupting chambers 17 and 18. The bridging member 2.1 is suitably operated by a mechanism 25. in normal operation the interrupting chambers 1'7 and 13 are immersed in a suitable insulating and are extinguishing liquid, such as circuit breaker oil, so that when the movable bridging contact 21 is in the lower open circuit position, the arcing contacts are effectively insulated from each ot er by a large oil gap. In general, circuit breakers of the type considered in Fig. l are provided with a plurality of similar pole structures, one for each phase of a polyphase electric circuit, however, only one such pole structure is shown in Fig. 1 and the circuit breaker will be described in detail as if it was of the single pole unit type.

Fig. 2 is an enlarged view in cross section of the left hand are extinguishing structure shown in Fig. l. The right hand are extinguishing structure is of similar design. In Fig. 2 the interrupting chamber contains a pair of interrupting or pressure generating contacts 30 and 31 of which the movable contact 30 is pivotally mounted at 32. Contacts 30, 31 are separated upon the downward movement of a push rod 33. A spring 34 upon the downward movement of push rod 33 and of bridging contact 21 and operating rod 24 in contact opening direction rapidly accelerates interrupting contact 30 in contact Opening direction. Movable contact 34) is attached at 35 to a link 36. Link 36 is pivotally mounted on push rod 33 by pin 37. The upper end of insulating rod 33 may be slotted to form a bifurcated portion and link 36 and contact 30 are arranged between these two prongs. The upper end of spring 34 rests against a fused shoulder 38 of the frame structure of the interrupting chamber 17. The circuit breaker structure it) may employ spring actuated interrupting contacts such as contacts 39, 31, alone or in combination with spring actuated oil pumps for the interruption of line charging currents and such low value of inductive currents as are not effectively interrupted by suicidal type devices.

Push rod 33 at its end remote from the bridging contact member 21 abuts against a push rod 39. Push rod 39 is provided with a valve stem 49, a spring biased valve element 41 forming a part of a spring biased piston 42. Piston 42 is arranged in a cylinder 43 of a pump 44. Cylinder 43 is open at its lower end so that oil ahead of piston 42 will be forced through the lower open end of cylinder 43 into a pressure chamber 45.

During a circuit closing operation of the interrupter, the bridging contact member 21 forces the push rod 33 upward. Push rod 33 in its upward movement rotates arcing contact 3t} counterclockwise to cause it to engage the slot wall sides of its fixed contact structure Push rod 33 in its upward movement to closed circuit position pushes rod 39 upward against the biasing action of the spring biased piston 42. The electrical circuit through this arc interrupting chamber 17 comprises lead-in conductor (not shown) arranged in the bushing 15, the support and the walls of chamber 45, flexible connector 46, movable interrupting contact 30, fixed interrupting contact 31, movable arcing contact 22, and bridging contact member 21.

The are interrupting chamber 17 utilizes two assemblies 59 and 51 of suitable shaped insulating plates which form part of the walls of the paths through which the arcs travel. These stacks of insulating plates are well known in the art. The fluid under pressure caused by the movement of piston 42 in breaker opening direction will flow through chamber 55 and assembly 56 to extinguish the arc drawn between contacts 36 and 31 and the pressure created by the arc drawn between contacts 19 and 22 wiil cause a fluid flow through assembly 51 which will aid in extinguishing the are between contacts 19 and 22.

During the opening operation, the bridging contact member 21 is moved downward by the operating mechanism 25. Mechanism 25 is released by the trip free mechanism it. As diagrammatically shown in Fig. l, the circuit breaker 1a is biased to open circuit position by any suitable separating means such as accelerating spring means 52 and shock absorber 53. The operating rod 2 is connected to the trip free operating linkage 14 through the operating mechanism 25.

The operating linkage 14 of the trip free mechanism comprises a lever 54 pivoted at 55 and a lever 56 pivoted at Levers 54 and 56 are interconnected by a toggle comprising two toggle elements 57 and 58. Toggle element 57 is pivotally connected to lever 56 by a pin carrying a roller 59, and toggle element 58 is pivotaliy connected at 613 to lever 54. Toggle elements 57 and 58 are pivotally joined together by a pin 61. Pin tii supports a roller 62 which is acted upon by an operating ram 63.

the contact closed position of the operating linkage 1 the upper position of pin 61 and roller 62 is controlled by an abutment 64. This abutment is made of any suitable resilient material and is adapted to minimize vibrations of the frame of the trip free mechanism 11 due to the impact of linkage 14 upon abutment 64. In the closed position of the circuit breaker it pin 61 forming the joint or connection between toggle elements 57 and 53 is supported by a spring biased prop 65. Spring 66 resets linkage 14 upon a trip free operation. Spring 66 is secured at one end of the frame of the trip free operating mechanism 11 and at the other end to a lug 67 of toggle element 58.

The circuit breaker 1G is opened by springs 52 and 53 upon a predetermined movement of a tripping mechanism 7t Tripping mechanism 70 comprises a first lever 71 pivoted at 72, a second lever 73 pivoted at 74, and a trip solenoid 75 comprising a plunger 76 adapted to act on lever 73. Plunger 76 can be operated either eiectrornagnetically by energizing solenoid 75 or mechanicaliy by manual means, i. e., by operation of a lever 77 pivoted at 78. Upon counterclockwise rotation of lever 73 about point '74, lever 71 is free to pivot about pin 72 in the counterclockwise direction under the action of a force component transmitted to it by roller 59. The counterclockwise rotation of lever 71 causes counterclockwise movement of lever 56 followed by collapse of the toggle formed by toggle elements 57 and 58 and return of lever 56 to the position shown to cause the separation of the circuit breaker contacts.

During a circuit breaker opening operation push rod 3i? moves upward and causes the counterclockwise rotation of lever 54. Rod 89 is pivotally mounted at one end thereof on lever 54 by means of pin 81 and to a crank 82 at the other end thereof. Crank 82 is secured to a shaft 83. A crank 84 mounted on shaft 83 is fastened at one end thereof to a shaft 35. Upon the movement to the right of shaft under the action of springs 52 and 53 and the upward movement of rod 80, crank 84 rotates crank 82 and shaft 33 clockwise. Shaft 85 is secured to a pin 87 upon which is mounted a pair of levers 88. Levers 88 are pivotally mounted on a shaft 89 arranged in bearings 90 which are mounted on a frame member 91. A lever 92 mounted on shaft 89 is pivotally connected to a link 93 by means of a pin 94. Link 93 is pivotally mounted on a lever 95. Lever 95 is pivotally mounted at one end thereof in a bearing 96 attached to frame 91 and pivotally mounted to a link 97. Link 97 is pivotally H attached at one end thereof to an extension 98 of lifting rod 24- and pivotally attached to a lever 99. Lever 99 is pivotally attached to a frame member 190. There is no fixed mechanical connection between the impulse spring assembly 53 and the lift rod 24 or its actuating linkage 95, 97 and 99. The lift rod 24 and extension 98 form a continuous, inflexible rod connection between the bridging contact member 21 and the lever 97 to which it is rotatably connected by a bearing pin. The lift rod 24 is actuated in straight line axial motion by lever 97 and abuts and engages impulse spring assembly 53 during its final breaker closing movement only. Shaft 102 is attached at one end thereof to pin 87 and at the other end to one end of the accelerating spring 52.

One reason for limiting the striking velocity of the movable bridging contact 21 on push rod 33 is to reduce the tremendous forces of impact, the most important of which are encountered at pins 35, 37 and 32 and in upper movable contact 30, due to the high rotational moment of inertia of contact 30.

The effect of these impact forces, if unrestrained, is destruction of the bearings at pins 35, 37 and 32 and deformation of the contact 36 by yielding in its intermediate section.

It is only until after the engagement of bridging contact 21 with push rod 33 that the spring forces due to contact actuating spring 34 and the actuating spring of oil pump 44 begin to be felt. This is after the impact forces have been dissipated. To overcome the spring forces during the remainder of the closing stroke it is necessar to reduce the retarding force of the speed limiter to substantially zero;

Conceivably, in an interrupting structure which includes a spring actuated pair of contacts such as 30, 31 but does not include a spring actuated oil pump such as 44; i. e., a pair of pressure generating contacts, the need for an extremely high rate of contact separation may impose spring loads near the end of the breaker closing stroke of a magnitude to compel the use of a speed controller to prevent damage or destruction to the circuit breaker structure.

In: order to limit the velocity of the circuit breaker moving contacts in closing direction to a predetermined value so' as to eliminate the possibility of damage due to high velocity impacts, the speed controller 12 is provided. Controller 12 is especially useful on circuit breakers with spring actuated oil pumps such as pump 44 for aiding the interrupting of line charging currents because the oil pump springs impose an extremely heavy load near the end of the closing stroke, thus requiring high pressures in the fluid operating motor 13 to eflect the final closing operation. If these high pressures in motor 13 acted uncontrolled throughout the stroke of motor 13 with nothing but the mass of movable linkages to act upon, extremely high velocity impacts would occur at the end of the closing'stroke.

Therefore, in accordance with this invention a new and improved speed controller 12 (more clearly shown in Figs. 4 and 5') is provided comprising an outer cylinder 1115 mounted on a fixed support and a coaxial inner cylinder 1'66 partly contained within one end of the outer cylinder 1%. A piston 167 is arranged in one end of the inner cylinler 1116 and is actuable by a push rod 108 mounted at one end thereof on lever 54 and at the other end thereof on hollow piston rod 109 of piston 1217 against a spring 1% arranged between piston Hi7 and a cap 193 which seals the lower end of the inner cylinder 186 and the controller 12 closed. The inner cylinder 166 contains a fluid of suitable viscosity such as oil and is provided with a first escape means 110. The escape means is preferably located in cylinder 1% and may be disposed in the piston 107 to provide a passage for fluid to flow from the inner cylinder 1% through the escape means 11d into the hollow piston rod 109 and through a plurality of orifices 115 provided in piston rod 109 to the inside of the outer cylinder 185' behind piston 167. The escape means 110 comprises a plate 113 having an orifice 111, which may be varied by using plates 113 having orifices of diflerent size.

Plate 113 is loosely mounted on pins 117 so that when the speed controller 12 is at rest or piston 107 is being actuated upward in contact opening direction, plate 113 will drop away from its seat 118 under the action of gravity or any suitable biasing means (not shown). Oil above piston 1137 will flow through orifice 111 and the gap formed between plate 113 and its seat 118 during a contact opening operation. Escape means 110' thus ofiers negligible retarding force to the opening velocity of the breaker. During a contact closing operation, piston 167 is actuated downward and plate 113 is forced against its seat 118'. The oil below piston 107 during its downward movement in contact closing direction is forced upward through orifice 111 offering high retarding force to high velocity movement of the arcing contacts.

During low velocity movement of the arcing contacts in contact closing direction orifice 111 is normally large enough so that the oil below piston 107 may move through orifice 111 freely without substantially retarding the movement of the contacts.

The orifice 11 1 is of such size that it provides a retarding force essentially equal to the force that can be exerted by the fluid motor 13 when the velocity of its piston has reached the predetermined maximum value to which it is to be limited.

One or more apertures 114 are provided in the lower part of inner cylinder 106 to provide a second escape means for rendering the escape means 110 ineffective to retard the final movement of piston 107. The escape means 114 upon piston 1G7 reaching a predetermined point in its travel in contact closing direction substantially removes all retarding force to further movement of piston 19'] or the circuit breaker contacts. When piston 107 reaches the point in the closing stroke corresponding to the point at which the spring loads or" the circuit breaker oil pumps 42 and the loads of the accelerating springs 52 and 53" are encountered, the escape means 114 provides an orifice which bypasses the fluid from inside the inner cylinder 106 under piston 137 and into the outer cylinder 1&5 back of the piston 107. I

This speed controller has the following desirable characteristics:

1. it prevents high velocity impacts at the end of circuit breaker closing stroke;

2; it otfers high retarding force to high velocities but negligible retarding force to low velocities;

3. it offers negligible retarding force to the opening velocity of the breaker;

4. it offers negligible retarding force during the latter part of the closing stroke when high accelerating spring loads, oil pump spring loads, or magnetic forces may be encountered.

Upon the collapse of the toggle formed by elements 57 and lever 5'4 is rotated counterclockwise. This counterclockwise rotation or" lever actuates push rod 89 upward and causes the clockwise rotation of cranks 82 and This movement of cranks and causes the triggering of mechanism 25 which causes the separation of the breaker arcing contacts by accelerating springs 52 and 53.

To close the circuit breaker and to return the trip 4 linkage to the position shown in Fig. 1, gas under pressure permitted to flow from a reservoir (not shown) through a passage 26 into a chamber 7 termed by castit s S and 2? on the upstream side of a piston 7 of fluid r 13. When the pressure in chamber 27 reaches edetermined value, piston 7 and ram 63 apply a force to roller es of linkage 1d. Toggle elements 57' and 53 in moving upward during a closing stroke of piston 7, rotate lever about its pivot point in the clockwise direction. That rotary motion of lever causes operating rod on to move downward. The downward movement of rod 89 causes cranks 32 and 84 and shaft 83 to be rotated counterclockwise. Counterclockwise rotation of crank actuates shaft to the left. The movement of shaft to the left causes counterclockwise rotation of levers 8S, crank 92, crank 93 and lever 95. Counterclockwise rotation of lever causes clockwise rotation of lever 97 which closes the circuit breaker contacts against the action of accelerating springs 5'2 and 53 and the biasing spring of piston 42.

When the toggle elements 57 and 58 reach prop 65 in their upward movement under the action of piston 7 and ram 63, pin 61 biases prop 65 clockwise and slides or it until roller reaches abutment s4. After pin 61 slides on prop 65, prop 65 rotates counterclockwise under the action of its biasing means do until it is in a position to support pin 61. Lever "/"l and trip latch 73 retain roller 55 in position adjacent stop The toggle formed by eiements 57 and 58 is retained in contact closed position by the combined action of prop 65', lever 71 and latch 73. A closing operation is completed when prop 65, lever 71, and latch 73 have locked the toggle elements in contact closed position. Then the supply of compressed gas to passage 26 may automatically be shut off.

In accordance with this invention the movement of the circuit breaker movable contacts during a closing operation is limited to predetermined velocities in order to eliminate the possibility of damage to the contacts and interrupting devices due to high velocity impacts. Upon the clockwise rotation of lever 54, rod 108, piston rod 7 109 and piston 107 are actuated downward. The oil below piston 197 is forced through orifice 111 in plate 113, hollow piston rod 11b9, orifice 115 into chamber 116 in outer cylinder 105. When piston 167 has been pushed down into the lower end of the inner cylinder 106 oil passes freely from the inner cylinder under piston M7 to the inner cylinder above piston 107 through escape means 114. The last portion of the movement of piston 107 of the speed controller 12 in contact closing direction is unretarded. Thus the speed controller 12 and particularly escape means 110 offer extremely high retarding forces when high closing velocities are approached but negligible retarding force to low closing velocities. The :speed controller and particularly escape means 114 offers negligible retarding force near the end of the closing stroke of the circuit breaker when high spring forces and magnetic forces are encountered. Controller 12 offers substantially no retarding force to opening velocities of the circuit breaker structure.

Although but one embodiment of the present invention has been illustrated and described, it will be apparent to those skilled in the art that various changes and modifications may be made therein without departing from the spirit of the invention or from the scope of the appended claims.

It is claimed and desired to secure by Letters Patent:

1. In combination: a circuit breaker comprising a pair of contacts, spring biasing means for separating said con; tacts, means for closing said contacts against the biasing effect of said separating means, and means for providing retarding forces to high velocity closing movement of said contacts and negligible retarding forces to low velocity movement of said contacts.

2. In combination: a circuit breaker comprising a pair of contacts, means for separating said contacts to draw an arc, a spring actuated oil pump for aiding arc extinction, means for closing said contacts against the biasing effect of said pump, and means for providing retarding forces to high velocity closing movement of said contacts and negligible retarding forces to low velocity movement of said contacts.

3. In combination: a circuit breaker comprising a pair of contacts, spring means for separating said contacts to draw an are, a spring actuated oil pump for aiding arc extinction, means for closing said contactsagainst the biasing etfect of said spring means and said pump, and means for roviding retarding forces to high velocity closing movement of said contacts, negligible retarding forces to low velocity movement of said contacts, and substantially no retarding force to the opening movement of said contacts.

4. In combination: a circuit breaker comprising a pair of contacts, spring means for separating said contacts to draw an arc, a spring actuated oil pump for aiding arc extinction, means for closing said contacts against the biasing effect of said spring means and said pump, and means for controlling said contact closing means comprising an outer cylinder, a coaxial inner cylinder partly contained within one end of said outer cylinder, a piston arranged in one end of said inner cylinder and actuable by said contact closing means, escape means arranged in said inner cylinder for retarding the initial movement of said piston and said contacts in breaker closing direction and means for rendering said escape means ineffective during the final movement of said piston.

5. In combination: a circuit breaker comprising a pair of contacts, spring means for separating said contacts to draw an arc, a spring actuated oil pump for aiding arc extinction, means for closing said contacts against the biasing eifect of said spring means and said pump, and means for controlling said contact closing means comprising an outer cylinder, a coaxial inner cylinder partly contained Within one end of said outer cylinder, a piston arranged in one end of said inner cylinder and actuated y S id Contact closing means, escape means for causing fluid to pass out of said inner cylinder, and means positioned in said inner cylinder to cause said escape means to retard only the initial movement of said contacts in breaker closing direction.

6. In combination: a circuit breaker comprising a pair of contacts, means for separating said contacts to draw an'arc, a spring actuated oil pump for aiding arc extinction, means for closing said contacts against the biasing effect of said spring means and said pump, and means for controlling said contact closing means comprising an outer cylinder, a coaxial inner cylinder contained within one end of said outer cylinder, a piston arranged in said inner cylinder and actuated by said contact closing means, a first escape means arranged in said piston for causing fluid to pass out of said inner cylinder, and a second escape means arranged in said inner cylinder, said first escape means being positioned in said inner cylinder to retard the initial movement of said contacts in breaker closing direction and said second escape means being positioned in said inner cylinder to substantially remove all retarding force to further movement of said contacts in closing direction.

7. In combination: a circuit breaker comprising a pair of contacts, means for separating said contacts to draw an are, a spring actuated oil pump for aiding arc extinction, means for closing said contacts against the biasing effect of said spring means and said pump, andmeans for controlling said contact closing means comprising an outer cylinder, a coaxial inner cylinder contained within one end of said outer cylinder, a piston arranged in said inner cylinder and actuated by said contact closing means, a first escape means arranged in said piston for causing the cushioning medium to pass out of said inner cylinder, and a second escape means arranged in said inner cylinder, said first escape means being positioned in said piston to provide retarding forces to high velocity closing movement of said contacts, negligible retarding forces to low velocity movement of said contacts and substantially no retarding force to the opening velocity movement of said contacts, said second escape means being positioned in said inner cylinder to remove substantially all retarding force to the final closing movement of said contacts.

8. In combination: a circuit breaker comprising a pair of contacts, spring means for separating said conta means for closing said contacts against the biasing E1 of said spring means, and means for controlling said con tact closing means comprising an outer cylinder, a coaxial inner cylinder partly contained within one end of said outer cylinder, a piston arranged in one end of said inner cylinder and actuable by said contact closing means, escape means arranged in said inner cylinder for retarding the initial movement of said piston and said contacts in breaker closing direction and means for rendering said escape means ineffective during the final movement of said piston.

9. In combination: a circuit breaker comprising a pair of arcing contacts, a pair of interrupting contacts, means for separating said arcing contacts to draw an arc, a first spring means for separating said interrupting contacts, an oil pump, a second spring means for actuating said oil pump to aid arc extinction, means for closing said contacts against the biasing effect of said first and second spring means, and means for providing retarding forces to said closing means from the time of actuation thereof until the biasing effects of said first and second spring means are encountered.

10. In combination: a circuit breaker comprising a pair of contacts, means for separating said contacts, means for closing said contacts against the eifect of said separating means, and means for providing a maximum retarding force to the initial closing movement of said contacts and negligible retarding force to the final closing movement of said contacts.

11. In combination: a circuit breaker comprising a pair of arcing contacts, a pair of pressure generating 2,"zes,424

contacts, means for separating said arcing contacts to draw an arc, spring means for separating said pressure generated contacts, means for closing said contacts against the biasing efiect of said spring means, and means for providing a maximum retarding force to the closin; movement of said contacts from the time said closing means are actuated until the biasing effect of said spring means is encountered and negligible retarding force to the final closing movement of said contacts.

References Cited in the file of this patent UNITED STATES PATENTS Prince Dec. 24, Van Sickle Dec. 19, Hubbard Sept. 18, Bartlett Aug. 5, Friedrich et a1. Dec. 9, Wallace et a1. Dec. 16,

Heintz Sept, 6, 

